The clinical characterization of an emerging vulvovaginal smooth muscle tumor harboring a nuclear receptor coactivator 2 (NCOA2) rearrangement represents a notable diagnostic breakthrough. Gynecologic pathologists frequently encounter challenges when evaluating rare lower genital mesenchymal lesions. Therefore, clinicians must recognize the morphologic, phenotypic, and genetic features of this rare neoplasm to avoid misdiagnosis.

Clinical Presentation of Vulvovaginal Smooth Muscle Tumor

Primary mesenchymal neoplasms of the vulva occur far less frequently than corresponding uterine smooth muscle tumors. Generally, affected patients are perimenopausal or postmenopausal women presenting with a painless or tender labial mass. In a recently reported case, a 56-year-old female noticed a slow-growing nodule in her right labium majus. Patients often report localized discomfort or swelling that clinically resembles a Bartholin cyst. Consequently, initial assessments frequently mistake these deep-seated lesions for simple inflammatory collections. Furthermore, diagnostic delay can occur because physical symptoms evolve gradually over several months. However, careful physical examination reveals a firm, well-circumscribed mass rather than a fluctuant fluid collection. Pelvic imaging, particularly magnetic resonance imaging, typically exhibits hyperintense T2 signals reflecting internal myxoid change. Thus, radiologists and gynecologists should maintain a high index of suspicion for rare solid neoplasms. Prompt recognition ensures complete surgical evaluation and prevents diagnostic errors. Ultimately, identifying these atypical presentations guides timely surgical intervention.

Histopathological Patterns and Microscopic Architecture

Under microscopic examination, this entity demonstrates a unique mixture of epithelioid and spindle cells. These cells arrange in short fascicles or small cohesive nests surrounded by abundant myxoid stroma. In addition, the prominent myxoid extracellular matrix imparts a distinctly pale, hypocellular appearance. Notably, microcystic spaces form a lace-like or reticular framework across the tumor tissue. Neoplastic cells possess round to ovoid shapes with moderate eosinophilic or clear cytoplasm and uniform vesicular nuclei. Importantly, the tumor lacks severe nuclear atypia, marked pleomorphism, and multinucleated tumor giant cells. Mitotic activity also remains extremely low throughout the lesion. For example, standard counting identifies virtually absent mitotic figures, with Ki-67 labeling measuring approximately one percent. Moreover, peripheral borders remain well demarcated without destructive infiltration into adjacent soft tissues. This bland cytological landscape clearly distinguishes the lesion from high-grade myxoid leiomyosarcomas. Consequently, pathologists must recognize these distinctive histological characteristics to prevent overcalling malignancy.

Immunohistochemical Profile and Estrogen Receptor Absence

Immunohistochemistry provides essential objective evidence confirming smooth muscle differentiation in lower genital tract tumors. Neoplastic cells show intense, diffuse cytoplasmic reactivity for smooth muscle actin, desmin, and h-caldesmon. As a result, this strong myogenic profile reliably excludes fibroblastic, neural, and melanocytic neoplasms. However, the immunophenotypic evaluation reveals an extraordinary finding regarding hormone receptor status. Most traditional vulvovaginal leiomyomas consistently express estrogen and progesterone receptors. In sharp contrast, this NCOA2-rearranged neoplasm displays complete negativity for estrogen receptors. This negative estrogen receptor status significantly expands the biological spectrum of female genital smooth muscle tumors. Furthermore, it demonstrates that smooth muscle differentiation does not strictly depend on hormone receptor signaling. Pathologists must also assess other markers, including CD34, S100 protein, and cytokeratins, which remain uniformly negative. Thus, combining comprehensive myogenic panels with hormone receptor studies establishes the correct diagnostic category. Accordingly, clinicians gain clarity regarding the true phenotypic nature of the lesion.

Molecular Hallmarks and NCOA2 Rearrangements

Recent molecular discoveries have revolutionized our diagnostic framework for rare genital mesenchymal tumors. Specifically, fluorescence in situ hybridization confirms recurrent structural rearrangements involving the NCOA2 gene on chromosome 8q13. In earlier described cases, NCOA2 fused directly with the MEF2D gene to generate an oncogenic driver. However, newer findings demonstrate NCOA2 rearrangements in the absence of MEF2D involvement. This critical observation proves that alternative partner genes can trigger identical morphological transformations. Functionally, NCOA2 serves as a transcriptional coactivator interacting with nuclear receptors to regulate gene expression. When rearranged, the resulting aberrant fusion product drives cellular proliferation and abundant myxoid matrix accumulation. Therefore, cytogenetic testing provides definitive confirmation when histological and immunohistochemical findings overlap. In addition, molecular validation prevents misdiagnoses when biopsy samples lack definitive architectural hallmarks. Consequently, specialized pathology centers must employ fluorescence in situ hybridization when encountering unusual myxoid vulvar lesions. Ultimately, molecular analysis ensures accurate classification and enhances our understanding of tumor pathogenesis.

Differential Diagnosis and Clinical Management Strategies

Clinicians and pathologists must distinguish this tumor from other myxoid vulvovaginal lesions. For example, aggressive angiomyxoma represents an important mimetic because it also occurs in vulvar soft tissues. However, aggressive angiomyxoma possesses thick-walled vessels and lacks uniform caldesmon immunoreactivity. Similarly, angiomyofibroblastoma features alternating cellularity and clusters around delicate blood vessels rather than true fascicles. Furthermore, physicians must exclude malignant myxoid leiomyosarcoma, which exhibits marked cytological atypia and brisk mitoses. Therapeutic management for NCOA2-rearranged tumors relies on complete local surgical excision with negative margins. Because these neoplasms behave in an indolent manner, wide radical vulvectomy and lymphadenectomy remain unnecessary. Adjuvant radiotherapy and cytotoxic chemotherapy are likewise inappropriate for this low-grade neoplasm. In addition, endocrine therapy offers no benefit due to negative estrogen receptor expression. Nevertheless, gynecologists should schedule regular postoperative surveillance to monitor for potential local recurrence. Thus, multidisciplinary coordination between surgical oncologists and pathologists optimizes patient outcomes and avoids aggressive overtreatment.

Frequently Asked Questions

What distinguishes this tumor from classic vulvar leiomyomas?

Classic vulvar leiomyomas typically present with intersecting bundles of uniform spindle cells and strongly express estrogen and progesterone receptors. In contrast, this emerging variant displays epithelioid cytomorphology, prominent myxoid matrix, and microcystic architecture. Furthermore, it completely lacks estrogen receptor expression while demonstrating distinct NCOA2 gene rearrangements. Recognizing these divergent phenotypic and cytogenetic hallmarks prevents clinicians from misinterpreting the mass as an aggressive myxoid sarcoma or an atypical myofibroblastic tumor.

Why is molecular confirmation of NCOA2 rearrangement clinically necessary?

Molecular testing using fluorescence in situ hybridization confirms diagnostic accuracy when histopathological features overlap with other myxoid neoplasms. Because entities like aggressive angiomyxoma and myxoid leiomyosarcoma carry different prognoses and surgical requirements, distinguishing them is vital. Identifying an NCOA2 rearrangement verifies this specific indolent smooth muscle entity, even when estrogen receptors are completely absent. Consequently, molecular confirmation prevents diagnostic confusion and prevents unnecessary radical surgical interventions or unindicated adjuvant toxicities.

What is the recommended surgical management and surveillance protocol?

Complete conservative surgical excision with histologically negative margins represents the definitive primary management. Because the tumor exhibits an exceptionally low proliferative index and benign clinical behavior, extensive radical vulvectomy and regional lymphadenectomy are unnecessary. However, because published medical literature regarding long-term outcomes remains limited, clinicians should establish routine postoperative surveillance. Regular pelvic examinations over a two- to five-year period ensure timely detection of potential local recurrences and ensure patient reassurance.

Disclaimer: This content is for informational and educational purposes only and should not be considered medical advice. Always consult a qualified healthcare provider for diagnosis and treatment decisions. Refer to the latest local and national guidelines for clinical practice.

References

1. Li L et al. Vulvovaginal Myxoid Epithelioid Smooth Muscle Tumor With NCOA2 Rearrangement: Case Report and Literature Review. Int J Gynecol Pathol. 2026 Oct 12. doi: 10.1097/PGP.0000000000001221. PMID: 42860365.
2. Tesarova P et al. The MEF2D::NCOA2 Fusion Defines a Distinct Emerging Vulvovaginal Myxoid Epithelioid Tumor With Smooth Muscle Differentiation. Am J Surg Pathol. 2025;49(3):301-310.
3. Nielsen GP, Rosenberg AE, Koerner FC, Young RH, Scully RE. Smooth-muscle tumors of the vulva. A clinicopathological study of 25 cases and review of the literature. Am J Surg Pathol. 1996;20(7):779-793.